Abstract

After the discoveries of Laue and Bragg the physics of crystals progressed very rapidly, both experimentally and theoretically. Taking the existence of regular arrangements of atoms in lattices for granted, Laue, Madelung, Born and others developed the theory of ideal crystals. This theory met with great success as far as certain special properties of crystals are concerned. However, at the same time it became apparent that its foundations were not broad enough to provide for a general scheme in which all the phenomena related to the crystalline state could be incorporated. The purpose of this paper is to show that this failure of the theory may have its origin in the fact that nobody seems to have considered seriously the question why crystals do exist at all. A tentative answer to this question will be given in the following. To obtain this answer it will be found that special emphasis must be laid on the problem of arriving at a clear understanding of the nature of the transitions gas-liquid, and liquid-crystal. The suggested solution also throws new light on the problem of the primary and the secondary (mosaic) structure in crystals.